There are alot of things you have to take into consideration.
1- The RSX-s is actually pretty weak until the motor is good and broke in. (it could be new)
2- I know that some gsr's could beat a stock rsx becuase sometimes you luck out and just get a good motor. (I swear my 00 blue si was almost as fast as my 99 gsr)
3- If you were at a light, you could smoke him off the line cause the stock rsx tires SUCK!

You can take this how you want, but I have owned both cars and my rsx is hella faster.